1. Field of the Invention
The present invention relates generally to a safety valve of a tank for storing and carrying oil or chemical substance, and more particularly to a safety valve installed in a tank of a vessel carrying oil or chemical substance to discharge supersaturated gas produced in the tank and to adjust an internal pressure to a normal level when a negative pressure is produced in the tank.
2. Description of the Related Art
A number of valves are registered as patents, and have been widely used. One example of such a valve is disclosed in U.S. Pat. No. 5,873,384 issued to Pedersen et al., in which a disc is fixed to a valve stem, and when the disc is raised, a free passage slot between a side of the disc and an inner side of the upper body is gradually decreased. Another example is disclosed in U.S. Pat. No. 5,060,688 issued to Sorensen, in which when a disc is raised, a free passage slot between a side of the disc and an inner side of the upper body is gradually increased.
According to the prior relief valve, because a small amount of the supersaturated gas in the tank is discharged at an early stage when the gas is discharged through the relief valve, the internal pressure of the relief valve is increased to a level higher than a discharged pressure of the gas, such that the safety of the tank cannot be secured.
Specifically, at an early stage when the supersaturated gas is discharged from the tank, the internal pressure of the relief valve is maintained at a level higher than the discharged pressure of the supersaturated gas. At a middle stage, the internal pressure of the relief valve is gradually decreased, so that the internal pressure is normally maintained. Therefore, the prior relief valve has no ideal construction. In addition, the valve is frequently adhered to a valve seat due to volatile steam and gas, chemical substance, salt or the like, such that the valve is not easily opened
Therefore, in order to solve the problems involved in the prior art, it is an object of the present invention to provide a safety valve of a tank for storing and carrying oil or chemical substance, in which at an early stage when a supersaturated gas is discharged from the tank, an internal pressure of the valve is no higher than a discharged pressure of the gas by discharging a lot of gas, thereby securing the safety, significantly reducing a hammering phenomenon, and preventing the adhesion of the valve-valve seat and the disc-lower body.
In order to achieve the above objects, according to one aspect of the present invention, there is provided a safety valve installed in a tank of a vessel carrying oil or chemical substance to discharge supersaturated gas produced in the tank and to adjust an internal pressure to a normal level when a negative pressure is produced in the tank; a lower body; an upper body mounted onto the lower body; a valve stem extended from the upper body to the lower body; and a disc provided on the valve stem and positioned between the upper and lower body to shut out a communication between the upper and lower body.
The disc has a groove on an underside thereof, with a protruded portion being formed along an edge of the disc, a Teflon (a trademark) bushing is interposed between the disc and the valve stem, and the disc has a large diameter than an internal diameter of the lower body. Teflon is a Dumont trademark for a low friction material of tetrafluoroethylene (TFE) polymer and/or fluorinated ethylene-propylene (FEP) resin.
The upper body has a straight portion on an internal lower edge thereof, the straight portion is formed in such a manner that until the disc is raised to a maximum stroke the portion is parallel with the disc, and a space is formed between a side of the disc and the straight portion of the upper body.
The upper body includes a valve stem lifting unit having a lug integrally formed on an external upper portion of the upper body, the lug coupled to a pair of supporting rods by a bolt, a lever inserted between the supporting rods and fixed by a pin 46a, an engaging member welded on an end of the lever, and a semicircular ring fixed to an inside of the engaging member.
When the valve is closed, a slanted flow path is formed between the protruded portion of the disc and a slanted surface of the lower body to smoothly discharge supersaturated gas.
The safety valve further comprises a vacuum valve including a disc adhered to a disc seat, a shaft 66 provided with a weight and the disc, and a knob engaged to an end of the shaft.
The disc has a slanted surface on an upper edge to assist the discharge of the gas.